This invention relates to improved stiffening means in manhole cover supports, that provide greater resistance to deformation and displacement occurring during and after installation of such cover supports into the existing manhole cover receiving structure, such as a manhole frame. The improvement of the invention is particularly suitable for those manhole cover supports that are expandable to provide a vastly improved grip against the housing of the manhole cover receiving structure. These manhole cover supports include split-rings, segmented rings and segmented rectilinear frames.
For simplicity the term "existing manhole cover receiving structure" is used here to refer to the existing, i.e., fixed in-place frame or other seating receptacle for a removable cover or grating that covers an access hole (i.e., hand hole, tool hole, manhole, catch basin or the like). The term "manhole cover" is used in this application to refer to a removable cover or grating over the access hole. The resulting assembly of a receiving structure and a manhole cover ordinarily is intended to bear vehicular traffic. The term "manhole cover support" or simply "cover support" here means a structure that fits over the existing manhole cover receiving structure, raises its grade, and thereby accommodates a cover or grating at the new elevated grade. The access hole covered usually is a utility enclosure serving, e.g., an electric, gas, water, sewer or storm drainage system.
The preponderance of manholes are circular (in street plan), have circular covers and have existing cover-receiving structures such as frames that have circular access holes, circular sills to support the cover, and circular lateral cover keepers (the latter also sometimes termed "collars"). Still others are polygonal, typically rectangular, in nature. In either case, it is desirable to increase the resistance of the cover support, in particularly the top of the cover support, from deformation. Accordingly,, this specification is directed to all manhole cover supports that have ring-like or polygonal, e.g., rectangular, annular elements which are adapted to interact with an existing cover-receiving structure.
Ordinarily a cover support finds its use when a roadway such as a street or highway is resurfaced with an added layer of paving material or repaved, typically with asphalt, concrete or sheet asphalt, to establish a higher grade than immediately before. A principal use for the instant cover support is expected to be in a municipality where axle loads up to 18,182 kg. may have to be resisted by many of these cover supports (as well as serious impact loads from vehicles and snow plows plus a variety of temperature effects, steam leaks,, spillage, etc.) without permitting a hazardous dislocation of the cover support or its cover. Often it is desirable also to cushion the cover for resisting wear or reducing noise, and/or to seal the cover and its cover support against a substantial and possibly overloading infiltration of surface water, e.g., storm drainage that otherwise would enter a sanitary sewer system at various manhole locations.
While the improvement of the invention applies to any manhole cover support, adjustability of the cover support in peripheral dimension and height is desirable for accommodating the wide range of specifications to be met. Consequently, the improvement of the invention is particularly advantageous for adjustable split-ring cover supports such as those disclosed in the parent application U.S. Ser. No. 07/596,255 filed Oct. 12, 1990, and also for adjustable rectangular and segmented ring manhole cover supports such as those disclosed in U.S. Pat. Nos. 4,966,489, 4,872,780, and 4,867,600 all of which are incorporated herein by reference.
The conventional split ring cover support today has a base ring that is practically uniform in its cross section. Perhaps the least expensive manhole cover support for a circular manhole is a conventional split-ring cover support like the one invented by A. H. R. McCoy. It is disclosed in U.S. Pat. No. 3,891,337 of Jun. 24, 1975, and shows a screw-operated expansion joint, the screw working against the reaction of an abutment projecting from the inside of the base ring. Related supports with various sorts of joint expander means for the split base ring have been developed since then, e.g., the Fier U.S. Pat. Nos. 4,097,171; 4,225,226; and 4,302,126 which show a conventional turnbuckle acting on pivotal eye bolts for the expansion joint and some lever-operated expansion joints, i.e., ones with a spreading link or a pivotally-mounted spreading toggle mechanism.
Segmented ring supports typified by U.S. Pat. No. 4,872,780 have at least on adjustable joint, provided with a spreader means such as a turnbuckle bolt to forcibly engage the housing of the manhole frame structure. The non-adjustable cover support structure of said patent is also significantly improved by the instant invention.
A typical rectangular support has gaps between opposing ends of the base portions that constitute the "sides" of the rectangle. Typically the gaps are at the corners to form adjustable joints between oblique mitered ends of the "sides". The joints include spreader means, such as a turnbuckle, for manipulating the peripheral dimension and base pressure against the reaction surfaces such as the surfaces of the existing collar or receiving element.
Operable service conditions include installing, adjusting, loading, unloading and otherwise handling manhole cover supports and removing the covers therefrom usually is done with powerful and indelicate tools such as picks, pinch bars, crowbars and the like. Deformation of the cover support can occur, particularly about its upper edge which is nearest the road surface. Also, the upper edge is usually the handiest area for applying tools and lifting forces. Deformations along the top are disadvantageous and render the opening of the support unfit for service. Hence, stiffness and resistance against deformation are primary concerns. The wheel loadings caused by vehicle traffic is another serious contributor to deformation and displacement of manhole cover supports.
On the other hand, a relatively light construction of the cover support, in comparison to the usual cast iron frame that usually supports the first manhole cover when the paving is laid, also desirable. To avoid sacrificing ruggedness, resistance to deformation and resistance to displacement, the main place for weight reduction is in the lateral keeper cover or in the base of the cover support. Clearly, the economics of manufacture, handling and installation all generally favor a lighter construction. Moreover, in order to accommodate full seating of the manhole cover within the manhole cover support that has been installed into the manhole cover receiving structure, e.g., manhole frame, specific design restrictions as to the thickness of the lateral cover keeper must be maintained. Therefore, a relatively thin wall keeper of the instant invention would normally be comprised of steel and is rarely more than about 0.1 inch (12 ga.) thick and is usually less. Steel keepers in such thin gauges as from 12 to 16 gauge are at times vulnerable to deformation throughout its structure, especially along the top rim of the keeper wall.
The instant invention is directed to improving the resistance of cover supports, particularly the upper edges thereof, to deformation without sacrificing the advantages of lighter construction. More particularly, the instant invention is directed to improving the entire resistance of all manhole cover supports to deformation and displacement caused by service conditions and vehicle traffic which would otherwise limit service life or cause outright failure.